[LeCow]

To support your point. I've used these weaknesses to break crypto algorithms in the past.

A typical example is the crapto-1 Mifare Classic algorithm used to encrypt NFC cards. The way they read from the shift register and combine the bits was dumb and it's complexity weakened the algorithm.

Another I've seen is using two sequential keys XORd against one another to produce and "encryption" key. Turns out reading from low entropic systems very quickly yields a similar enough key that when XORd, partially removes the first one.